1. Field of the Invention
The present invention relates to a substrate processing system and a substrate cleaning apparatus, and to a substrate processing system including the substrate cleaning apparatus for removing foreign matter adhering to a rear surface or a periphery of the substrate.
2. Description of the Related Art
Conventionally, in a substrate processing apparatus for performing predetermined processing on a substrate which is a semiconductor wafer (hereinafter referred to simply as “wafer”), pieces of metal, such as metal pieces of aluminum, resulting from contact between the wafer and a mounting stage on which the wafer is mounted, and reaction products, such as fluorocarbon-based polymers or the like, resulting from processing gas reactions are generated. The foreign matter (particles) adheres to the wafer, thereby reducing the quality of a semiconductor device formed on a surface of the wafer.
As a method for removing particles adhered to the wafer, a wet cleaning method is known in which a wafer that has undergone etching processing is cleaned using a hydrofluoric acid solution or pure water in a wet processing chamber (see, for instance, Japanese Laid-Open Patent Publication (kokai) No. H4-14222). In another known method, a plurality of wafers is cleaned by immersion processing in a cleaning tank filled with a cleaning solution such as an ammonia solution or a hydrofluoric acid solution or the like. According to these methods, it is possible to remove particles which have adhered to the wafers during etching processing.
However, since the above-described wet cleaning method mainly involve spraying pure water or the like towards a front surface of the wafer, particles adhering to the rear surface and bevel polymer adhering to the periphery (bevel portion) of the wafer cannot be removed.
Since the particles adhering to the rear surface of the wafer cause the wafer to rise when the wafer is mounted on the mounting stage, when a photoresist applied on the front surface of the wafer is exposed in a lithography process, the focus position fails to match the photoresist position, and the exposure cannot be accurately performed. Moreover, when the wafer is moved at the front of a lens in an immersion lithography apparatus, the bevel polymer at the periphery of the wafer passes through ultra pure water that exists between the wafer and the lens. At this point, the bevel polymer can, on occasion, detach and mix with the ultra pure water, the detached bevel polymer blocks light, and hence the exposure cannot be accurately performed. Also, a residual photoresist formed prior to the lithography process may be left on the periphery of the wafer, and mix with the ultra pure water in the same way as the bevel polymer. Consequently, there is a problem of reducing the quality of the semiconductor device manufactured from the wafer.
The wafers which have undergone the etching processing are transferred in a sealed vessel such as a FOUP (Front Opening Unified Pod) which holds the plurality of wafers in parallel with one another. However, there is a problem in that foreign matter (particles, polymer) detaches from rear surfaces or periphery of upper wafers in the FOUP, and drops and adheres to the front surfaces of lower wafers. This causes a problem of reducing, the quality of semiconductor devices manufactured from the lower wafers.
In the above-described method for immersing a plurality of wafers in the cleaning tank, it is possible to remove not only the particles on the front surface of a wafer, but also the particles on the rear surface of the wafer and the bevel polymer on the periphery of the wafer. However, there is a problem in that the removed particles remain in the cleaning solution and may therefore re-adhere to the wafers (cross-contamination), causing a problem of reducing the quality of semiconductor devices.
There is a further problem with the above-described wet cleaning method in that, since the flow of pure water in the wet cleaning is not controlled, even if the particles on the rear surface of a wafer and the bevel polymer are removed, the removed particles and bevel polymer re-adhere to the front surface of adjacent wafers, for instance the surface of wafers being simultaneously cleaned, the removed particles and bevel polymer thus causing reduction of the quality of semiconductor devices.